Method for configuring phich carrier linkage

ABSTRACT

There is provided a method of configuring the downlink component carrier between one or more linkage methods for PHICH reception on User Equipment (UE), which is configured for carrier aggregation, over a mobile communication network. This method includes (a) providing an indicator, and (b) determining whether the PHICH carrier linkage should be dynamic linkage or cell specific, based on the value of the indicator.

TECHNICAL FIELD

The present invention relates to wireless communications systems, andmore particularly to a method for configuring the downlink componentcarrier between one or more Physical Hybrid-ARQ Indicator Channel(PHICH) carrier linkage methods.

BACKGROUND ART

Long Term Evolution-Advanced (LTE-A) is an evolving mobile communicationstandard which aims to take advantage of 3G mobile communicationsdevices. A feature of LTE-A is carrier aggregation where two or morecomponent carriers are aggregated in order to support wider transmissionbandwidths.

It is thought that carrier aggregation will be User Equipment (UE)specific, i.e. each UE in the same cell in a mobile communicationnetwork may have different configuration of carrier aggregation.

If the carrier aggregation is symmetric (i.e. same number of downlinkcomponent carriers and uplink component carriers), the downlink(DL)/uplink (UL) component carriers are typically associated in pairs ina cell-specific manner. However, in the case of asymmetric carrieraggregation, more than one DL component carriers may be associated in acell-specific manner with a UL component carrier if there are more DLcomponent carriers than UL component carriers and vice versa.

Once a UE is configured with carrier aggregation, the UE is capable ofsimultaneously receiving or transmitting on all the component carriersthat are aggregated. Thus, the UE may be scheduled over multiplecomponent carriers simultaneously.

Typically, UE is only permitted to transmit on Physical Uplink SharedChannel (PUSCH) on a particular UL component carrier after it hasreceived an UL grant. After the UE has transmitted data on PUSCH on theUL component carrier, ACK/NACK is expected to be transmitted from theassociated eNodeB. A problem that arises is which DL component carriershould be used for the PHICH transmission when there are more than oneDL component carriers available.

The issue of PHICH carrier linkage is also related to the issue ofPhysical Downlink Control Channel (PDCCH)-to-PUSCH linkage currentlybeing considered in 3GPP.

There have been attempts at two options to solve the problem of PHICHcarrier linkage, namely: (1) DL component carrier for PHICH transmissionbeing the same as that used for the transmission of the UL grant; or (2)DL component carrier for PHICH transmission being linked to the ULcomponent carrier used for PUSCH transmission in a cell-specific manner.

SUMMARY OF INVENTION Technical Problem

A problem with option 1 is that it is not always beneficial to force thePHICH transmission to be on the DL component carrier where the UL grantwas transmitted (particularly in a heterogeneous network which is commonin mobile communications networks). Further, there is a potentialfurther problem in that the total PHICH resources in each componentcarrier are semi-statically configured (via the Physical BroadcastChannel) and hence the PHICH capacity cannot be adjusted dynamically. IfPDCCH and the corresponding PHICH can be scheduled on any DL componentcarrier dynamically, a significant amount of PHICH resources may need tobe provisioned for each component carrier in order to prevent PHICHblocking (where PHICH cannot be scheduled due to the lack of resources).However, the utilization of the PHICH resources could be low since onlya relatively small number of PHICH resources compared to the total PHICHresources available will be used at any one time.

Another problem with option 1 is when there are two UL grants for twodifferent UEs transmitted on the same DL component carrier, grantingPUSCH transmissions on two separate UL component carriers. PHICHresource collision may occur if the lowest of UL Physical Resource Block(PRB) indices and the Demodulation Reference Signal (DM RS) cyclicshifts for each UL component carrier coincide. While this collision maybe avoided via assignment of different DM RS cyclic shift in the ULgrants, it also means that for each UL component carrier, one fewer UEcan be spatially multiplexed in the UL for UL Multi-User Multiple-InputMultiple-Output (MU-MIMO) operation.

Furthermore, option 2 is not effective when PHICH needs to be protectedfrom a DL component carrier with high interference (e.g. particularly ina heterogeneous network which is common in mobile communicationsnetworks).

In light of the above, it would be desirable to provide, for a UE thatis carrier aggregation enabled, a downlink (DL) component carrier usedfor Physical Hybrid-ARQ Indicator Channel (PHICH) transmission to beconfigurable at the User Equipment (UE).

It will be appreciated that a reference herein to any matter which isgiven as prior art is not to be taken as an admission that that matterwas, in Australia or elsewhere, known or that the information itcontains was part of the common general knowledge as at the prioritydate of the claims forming part of this specification.

Solution to Problem

With this in mind, one aspect of the present invention provides a methodof configuring the downlink component carrier between one or morelinkage methods for PHICH reception on User Equipment (UE) over a mobilecommunication network, the UE configured for carrier aggregation,including the steps of:

(a) providing an indicator;

(b) determining whether the PHICH carrier linkage should be dynamiclinkage or cell specific, based on the value of the indicator.

Preferably, the indicator is a single bit in a signal. Preferably, theindicator is a single bit located in the uplink (UL) grant.

Preferably, the indicator is a single bit located in DCI formats for theUL grant.

Preferably, the indicator bit is introduced in DCI formats for UL grantand the indicator bit only exists in DCI formats if a PDCCH carrierindicator also exists.

Preferably, the indicator is a single bit located in the higher layersignalling.

Preferably, the higher layer signalling includes the Radio ResourceControl (RRC) signalling, or Medium Access Control (MAC) signalling.

Preferably, if at step (b), the PHICH carrier linkage should be dynamic,the method further includes the step of transmitting on the downlink(DL) component carrier used for the UL grant transmission.

Preferably, the method further includes the step of an eNodeB associatedwith the mobile communication network setting the PHICH carrier linkageas determined in step (b).

Advantageous Effects of Invention

Advantageously the invention enables, in the event that carrieraggregation is configured with a particular UE, the downlink componentcarrier to be used for PHICH transmission and is configurable at theuser equipment (UE) between two linkage methods, namely a method that isbased on the DL component carrier used for the UL grant and a methodthat is based on cell-specific UL/DL component carrier linkage.

In a further advantage, the present invention only incurs minimal costin terms of signalling to the UE (e.g., only one bit in the DCI formatsif it is explicitly signalled).

Advantageously, if the PHICH carrier indicator bit is introduced in DCIformats for UL grant, it only needs to exist in DCI formats with PDCCHcarrier indicator and this arrangement ensures that the total number ofblind decoding attempts required to be performed by the UE is notaffected by the introduction of the PHICH carrier indicator bit.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1A]

FIG. 1A is a schematic diagram of a UL grant in an existing LTE-Asystem.

[FIG. 1B]

FIG. 1B is a schematic diagram of a UL grant of the present invention.

[FIG. 2]

FIG. 2 is schematic diagram of carrier aggregation having PHICH dynamiclinkage and cell-specific linkage according to the invention.

[FIG. 3]

FIG. 3 is a flow diagram of the method of the present invention.

DESCRIPTION OF EMBODIMENTS

The following description refers in more detail to the various featuresand steps of the present invention. To facilitate an understanding ofthe invention, reference is made in the description to the accompanyingdrawings where the invention is illustrated in a preferred embodiment.It is to be understood however that the invention is not limited to thepreferred embodiment illustrated in the drawings.

Referring now to FIG. 1A, there is shown a schematic diagram of a ULgrant in an existing LTE-A system. In this case, a sub-frame 100includes a DCI payload 105 but does not include a PDCCH carrierindicator field. Also shown is an alternative sub-frame 110 whichincludes a DCI payload 105, but this time includes a PDCCH carrierindicator field 115.

FIG. 1B is a schematic diagram of a UL grant of the present invention.Also shown is a sub-frame 100 which includes a DCI payload 105. Asub-frame 110 which includes a DCI payload 105 and a PDCCH carrierindicator field 115 is also shown. Further included is a PHICH carrierindicator bit 120. The PHICH carrier indicator bit 120 only exists ifthe PDCCH carrier indicator field 115 also exists in the UL grant. Inparticular, the present invention introduces a single bit, namely thePHICH carrier indicator bit 120 in the UL grant or alternatively in thehigher layer signalling (e.g., radio resource control signalling) toindicate if the PHICH carrier linkage should be based on the DLcomponent carrier used for the UL grant (for ease of reference referredto as dynamic linkage) or the Cell-specific UL/DL component carrierlinkage (for ease of reference referred to as cell-specific linkage).Advantageously, if the PHICH carrier indicator bit 120 is introduced inDCI formats for UL grant, it only needs to exist in DCI formats withPDCCH carrier indicator field 115 as shown in the sub-frame 110 of FIG.1B. Advantageously, this arrangement ensures that the total number ofblind decoding attempts required to be performed by the UE is notaffected by the introduction of the PHICH carrier indicator bit 120.

The operation using the PHICH carrier indicator bit 120 is as follows:for example, the cell-specific linkage can be based on the cell-specificUL/DL component carrier pairing (according to the default transmitreceive separation or the UL-Carrier Freq parameter in SystemInformation Block 2 (SIB2) or be based on high-layer signalling, such asRRC, broadcasted to all UEs in the cell.

Preferably an eNodeB (not shown) sets the PHICH carrier linkage to bedynamic or cell-specific according to its need. If the PDCCH carrierindicator field 115 is configured by the eNodeB and if the eNodeB sendsan UL grant with the PDCCH carrier indicator field 115 and the PHICHcarrier indicator bit 120 indicating cell-specific linkage, the UE, upondetection of the UL grant and the PHICH carrier indicator bit 120, shallassume the DL component carrier for the PHICH is determined bycell-specific linkage with the UL component carrier used for thecorresponding PUSCH transmission.

Similarly, if the eNodeB uses the PHICH carrier indicator bit 120 toindicate the dynamic linkage to the UE, then the UE assumes that thePHICH is to be transmitted on the DL component carrier that was used fortransmission of the UL grant.

This is best shown in FIG. 2 which is a schematic diagram of carrieraggregation having PHICH dynamic linkage and a cell-specific linkageaccording to the invention. FIG. 2 includes two DL carrier components200 (DL CC #0 and DL CC #1) and two UL carrier components 205 (DL CC #0and DL CC #1). UL CC #0 and UL CC#1 are linked to DL CC #0 and DL CC #1respectively by a cell-specific linkage 220. Alternatively, UL CC #1 andDL CC #0 are linked via dynamic linkage 215. As an example, the UL grantfor UL CC #1 is transmitted in DL CC #0. If the PHICH carrier indicatorbit 120 is set to indicate dynamic linkage, then the corresponding PHICHis transmitted on DL CC #0. Otherwise, if cell-specific linkage isindicated via the PHICH carrier indicator bit 120, then thecorresponding PHICH is transmitted on DL CC #1. Advantageously theinvention enables, in the event that carrier aggregation is configuredwith a particular UE, the DL component carrier to be used for PHICHtransmission and is configurable at the UE between two linkage methods,namely a method that is based on the DL component carrier used for theUL grant and a method that is based on cell-specific UL/DL componentcarrier linkage.

In a further advantage the arrangement of the present invention exploitsthe advantages provided by the two methods, in particular, the inventionenables cell specific UL/DL component carrier linkage that allowsdecoupling of PDCCH scheduling and PHICH scheduling. As a result, thePDCCH scheduling across component carriers can be dynamic and theconfiguration of total PHICH resources available for each componentcarrier can be relatively static. A further advantage of the presentinvention enables PHICH scheduling flexibility when needed, by allowingPHICH to be transmitted on the DL component carrier that was used fortransmission of the UL grant which can also be flexible through the useof the PHICH carrier indicator bit 120. This is advantageous fordeployment scenarios (e.g. in heterogeneous networks) where some DLcomponent carriers may be experiencing high interference and the controlchannels (PDCCH and PHICH) of those interference-dominated DL componentcarriers need to be protected by transmitting them on another DLcomponent carrier with lower interference.

A further advantage of the present invention is to provide flexibleassociation of UL/DL component carriers for PHICH transmission whenUE-specific asymmetric carrier aggregation is configured in such a waythat cell-specific UL/DL component carrier linkage cannot be applied.

In a further advantage, the present invention only incurs minimal costin terms of signalling to the UE (e.g., only one bit in the DCI formatsif it is explicitly signalled).

FIG. 3 shows the method 300 of the present invention. At step 305 the UEdetermines whether or not the DCI format for UL grant (e.g. DCI format0) is to contain the PDCCH carrier indicator field 115 and the PHICHcarrier indicator bit 120. This step can be performed via higher layersignalling, such as via RRC, directly to the UE. If at step 305 it isdetermined that the PDCCH carrier indicator field 115 exists in the DCIformat for UL grant, then control moves to step 310 where, in asub-frame n, the UE detects and decodes UL grant with the PDCCH carrierindicator field 115 and the PHICH carrier indicator bit 120 on a DLcomponent carrier. Control then moves to step 315, in a sub frame n+4,where the UE transmits PUSCH on the UL component carrier indicated bythe PDCCH carrier indicator field 115. Control then moves to step 320where the UE determines if the PHICH carrier indicator bit 120 (decodedat step 310) indicates that dynamic linkage or cell-specific linkageshould be used. If at step 320 it is determined that the PHICH carrierindicator bit 120 indicates that dynamic linkage should be used, controlmoves to step 325, in a sub-frame n+8, where the UE detects and decodesPHICH on the same DL component carrier as was used for the UL grantdetected at step 310. The UE identifies its PHICH resource on the DLcomponent carrier (PHICH group index and sequence index in the same wayas release 8 of LTE) and detailed in Section 9.1.2 of TS36.213 v8.7.0,in which the PHICH resource is determined from lowest index PhysicalResource Block (PRB) of the uplink resource allocation and the 3-bituplink demodulation reference symbol (DMRS) cyclic shift associated withthe PUSCH transmission, both indicated in the PDCCH with DCI format 0granting the PUSCH transmission.

The PHICH resource is identified by the index pair (n^(group) _(PHICH),n^(seq) _(PHICH)) where n^(group) _(PHICH)is the PHICH group number andn^(seq) _(PHICH) is the orthogonal sequence index within the group asdefined by:

n ^(group) _(PHICH)=(I ^(lowest) ^(—) ^(index) _(PRB) _(—) _(RA) +n_(DMRS))mod N ^(group) _(PHICH) +I _(PHICH) N ^(group) _(PHICH)

n ^(seq) _(PHICH)=(└I ^(lowest) ^(—) ^(index) _(PRB) _(—) _(RA) /N^(group) _(PHICH) ┘+n _(DMRS)) mod 2 N ^(PHICH) _(SF)

where

-   -   n_(DMRS) is mapped from the cyclic shift for DMRS field in the        most recent DCI format 0 for the transport block associated with        the corresponding PUSCH transmission. For a semi-persistently        configured PUSCH transmission on subframe n in the absence of a        corresponding PDCCH with a DCI Format 0 in subframe n-k_(PUSCH)        or a PUSCH transmission associated with a random access response        grant, n_(DMRS) is set to zero where k_(PUSCH) is as defined in        section 8 in TS36.212.    -   N^(PHICH) _(SF) the spreading factor size used for PHICH        modulation as described in section 6.9.1 in TS36.211.    -   I^(lowest) ^(—) ^(index) _(PRB) _(—) _(RA) is the lowest PRB        index in the first slot of the corresponding PUSCH transmission    -   N^(group) _(PHICH) is the number of PHICH groups configured by        higher layers as described in section 6.9 of TS36.211,

${\bullet \; I_{PHICH}} = \left\{ \begin{matrix}1 & \begin{matrix}{{for}\mspace{14mu} {TDD}\mspace{14mu} {{UL}/{DL}}\mspace{14mu} {configuration}\mspace{14mu} 0\mspace{14mu} {with}\mspace{14mu} {PUSCH}} \\{{{transmission}\mspace{14mu} {in}\mspace{14mu} {subframe}\mspace{14mu} n} = {4\mspace{14mu} {or}\mspace{14mu} 9}}\end{matrix} \\0 & {otherwise}\end{matrix} \right.$

Alternatively, if at step 320 the UE determined the PHICH carrierindicator bit 120 indicated cell-specific linkage, control moves to step330 where, in a sub-frame n+8, the UE decodes the PHICH on the DLcomponent carrier with cell-specific association with UL componentcarrier used for PUSCH transmission as determined at step 315. The UEidentifies its PHICH resource on the DL component carrier (PHICH groupindex and sequence index) in the same way as LTE release 8 as describedabove.

If at step 305 the UE determines it is not required to detect UL grantwith the PDCCH carrier indicator field 115 (e.g. sub-frame 100 as shownin FIG. 1A or 1B) control moves to step 335 where, in sub-frame n, for aDL component carrier the UE detects and decodes UL grant without thePDCCH carrier indicator field (115) and the PHICH carrier indicator bit(120) on a DL component carrier. Control then moves to step 340 where,in a sub-frame n+4, the UE transmits PUSCH on the UL component carrierwhich is linked to the DL component carrier in a cell-specific manner(cell-specific being the default method). Advantageously, without thePDCCH carrier indicator, selecting cell-specific as the default methodprovides the simplest method for the UE to determine which UL componentcarrier is associated with a DL component carrier.

Control then moves to step 345 where, in a sub-frame n+8, the UE detectsand decodes the PHICH on the DL component carrier which is linked to theUL component carrier used for PUSCH transmission in step 340 (which isthe same as the DL component carrier where the UL grant was detected instep 335). The UE identifies its PHICH resource on the DL componentcarrier (PHICH group index and sequence index) in the same way as longterm evolution release 8 as described above.

Advantageously, a single PHICH carrier indicator bit 120 efficientlyallows two different methods of PHICH carrier linkage to be configured.

Although the exemplary embodiments of the invention have been disclosedfor illustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible withoutdeparting from the scope of the present invention. Therefore, thepresent invention is not limited to the above-described embodiments butis defined by the following claims.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority fromAustralian provisional patent application No. 2009903829, filed on Aug.14, 2009, the disclosure of which is incorporated herein in its entiretyby reference.

INDUSTRIAL APPLICABILITY

The present invention is applicable to wireless communications systems,and more particularly to a method for configuring the downlink componentcarrier between one or more Physical Hybrid-ARQ Indicator Channel(PHICH) carrier linkage methods.

REFERENCE SIGNS LIST

100, 110 SUB-FRAME

105 DCI PAYLOAD

115 PDCCH CARRIER INDICATOR FIELD

120 PHICH CARRIER INDICATOR BIT

200 DL CARRIER COMPONENT

205 UL CARRIER COMPONENT

215 DYNAMIC LINKAGE

220 CELL-SPECIFIC LINKAGE

1. A method implemented in a wireless communication network ofconfiguring a downlink (DL) component carrier between one or morelinkage methods for PHICH (physical hybrid-ARQ (automatic repeatrequest) indicator channel) reception on user equipment (UE), the UEbeing configured for carrier aggregation, the method comprising: (a)providing an indicator from a base station to the UE; (b) determining,at the UE and based on a value of the indicator, whether a PHICH carrierlinkage is either dynamic or cell specific; and upon a determinationfrom said determining step that said PHICH carrier linkage is dynamic,transmitting a PHICH on a DL component carrier used for uplink (UL)grant transmission, and upon a determination from said determining stepthat said PHICH carrier linkage is cell specific, linking a DL componentcarrier used for PHICH transmission to an UL component carrier used forPUSCH transmission in a cell-specific manner.
 2. The method of claim 1,wherein the indicator is a single bit in a signal.
 3. The method ofclaim 1, wherein the indicator is a single bit located in an uplink (UL)grant.
 4. The method of claim 1, wherein the indicator is a single bitlocated in a DCI (downlink control information) format for an uplink(UL) grant.
 5. The method of claim 4, wherein if the indicator bit isintroduced in the DCI format for the UL grant, the single bit exists inthe DCI format only if a PDCCH (Physical Downlink Control Channel)carrier indicator exists.
 6. The method of claim 1, wherein theindicator is a single bit located in higher layer signalling.
 7. Themethod of claim 6, wherein the higher layer signalling includes theradio resource control (RRC) signalling or medium access control (MAC)signalling.
 8. The method of claim 1, wherein, if at step (b) the PHICHcarrier linkage is determined as dynamic, the following further step isperformed: transmitting a PHICH on the DL component carrier used foruplink (UL) grant transmission.
 9. The method of claim 1, furthercomprising: setting, at the base station, the PHICH carrier linkage asdetermined in (b).
 10. A method implemented in user equipment (UE) usedin a wireless communication network, of configuring a downlink (DL)component carrier between one or more linkage methods for PHICH(physical hybrid-ARQ (automatic repeat request) indicator channel)reception, the UE being configured for carrier aggregation, the methodcomprising: (a) receiving an indicator from a base station; (b)determining whether a PHICH carrier linkage is either dynamic or cellspecific, based on a value of the indicator, wherein, upon adetermination from said determining step that said PHICH carrier linkageis dynamic, a same DL component carrier as that used for transmission ofthe UL grant is used for PHICH transmission, and wherein, upon adetermination from said determining step that said PHICH carrier linkageis cell specific, the DL component carrier for PHICH transmission islinked to the UL component carrier used for PUSCH transmission in acell-specific manner.
 11. The method of claim 10, wherein the indicatoris a single bit in a signal.
 12. The method of claim 10, wherein theindicator is a single bit located in an uplink (UL) grant.
 13. Themethod of claim 10, wherein the indicator is a single bit located in aDCI (downlink control information) format for an uplink (UL) grant. 14.The method of claim 13, wherein if the single bit for the indicator isintroduced in the DCI format for the UL grant, the single bit exists inthe DCI format only if a PDCCH (Physical Downlink Control Channel)carrier indicator exists.
 15. The method of claim 10, wherein theindicator is a single bit located in higher layer signalling.
 16. Themethod of claim 15, wherein the higher layer signalling includes theradio resource control (RRC) signalling or medium access control (MAC)signalling.
 17. The method of claim 10, wherein, if at (b) the PHICHcarrier linkage is determined as dynamic, the following further step isperformed: receiving a PHICH on the DL component carrier used for unlink(UL) grant transmission.
 18. The method of claim 10, further comprising:setting the PHICH carrier linkage as determined in (b).
 19. A methodimplemented in a base station used in a wireless communication network,of configuring a downlink (DL) component carrier between one or morelinkage methods for PHICH (physical hybrid-ARQ (automatic repeatrequest) indicator channel) reception on user equipment (UE), the UEbeing configured for carrier aggregation, the method comprising:providing an indicator to the UE, wherein the UE determines whether aPHICH carrier linkage, based on a value of the indicator, is eitherdynamic or cell specific, wherein, when said PHICH carrier linkage isdetermined as dynamic, a same DL component carrier as that used fortransmission of the UL grant is used for PHICH transmission, andwherein, when said PHICH carrier linkage is determined as cell specific,the DL component carrier for PHICH transmission is linked to the ULcomponent carrier used for PUSCH transmission in a cell-specific manner.